Data link communications systems are used to facilitate data communications between pilot, aircraft, and air traffic control centers (ATCs) and airline operations centers (AiOCs). Communications between an aircraft and an air traffic control center may include ATC messages, e.g. requests and clearances for changes to flight paths, and aircraft status reports. Communications between aircraft and airline operations centers may include aeronautical operational control (AOC) messages (e.g. about weather updates, flight plans, weight and balance data, etc.) and airline administrative control (AAC) messages (e.g. including departure and arrival data such as out of gate, off the ground, on the ground, and into the gate times). Controller-Pilot data link communications (CPDLC) systems facilitate communications between pilots and air traffic control centers to more efficiently manage an increasing density of aircraft, e.g. in the U.S. and European airspace.
There are two versions of controller-pilot data link communications systems for ATC messaging used in the world today. The two version of CPDLC provide similar functionality but use different communications protocols which are not interoperable. In the U.S., Future Air Navigation System 1/A (FANS 1/A) CPDLC is a standard controller-pilot data link communications system. FANS 1/A CPDLC employs aircraft communications addressing and reporting system (ACARS) protocol to send and receive messages. The ACARS protocol originated from a Telex format and is a character oriented protocol. FANS 1/A typically employs the ACARS protocol over an aviation VHF link control (AVLC or AOA) which sends and receives ACARS protocol messages, between an aircraft and ATC or AOC, on VHF data link mode 2 (VDL-Mode 2) at a data rate of 31.5 kbps. Alternatively, FANS 1/A can also employ Plain Old ACARS by sending and receiving ACARS protocol messages using a lower data rate, 2.4 kbps, VHF data link. In another alternative, FANS 1/A is capable of sending and receiving ACARS protocol messages, e.g. between an aircraft, and an ATC and/or AOC, over HF or SATCOM data links.
In Europe, a different system, Protected Mode-CPDLC (PM-CPDLC) is used to communicate data messages between an aircraft and an ATC. PM-CPDLC employs an Aeronautical Telecommunications Networks/OSI, or ATN/OSI, protocol to send and receive messages. PM-CPDLC messages are also sent and received using VDL-Mode 2. PM-CPDLC utilizes the ATN/OSI protocol on VDL-Mode 2. However, because FANS 1/A CPDLC uses the ACARS protocol and PM-CPDLC uses the ATN/OSI protocol, the two systems are incompatible.
Most aircraft have avionics equipment that implements one version of CPDLC. For example, aircraft of U.S. operators typically have equipment that implements FANS 1/A CPDLC; aircraft of European operators typically have equipment that implements the PM-CPDLC system. Thus, when an aircraft of a U.S. operator departs U.S. air space and enters European airspace, the pilots must rely on less efficient voice communications to communicate with the local air traffic control center.
Aircraft operators are either unable to upgrade avionics on some of their aircraft to support both versions of CPDLC and to permit graceful transition between CPDLC ATC messaging systems, or are reluctant to perform such an upgrade when available because of the cost. Therefore, there is a need for a less costly system that can be retrofitted to these older aircraft that would permits pilots to transition between the two versions of CPDLC systems.